Overview

Our long-term objectives remain to understand hepatic epithelial function and dysfunction. We continue to focus on cholangiocytes because of their pathobiologic importance and the novel techniques we have developed to study cholangiocyte function. Here we concentrate on the cholangiociliopathies, a group of incurable genetic diseases characterized by cholangiocyte-derived liver cysts (with or without fibrosis) resulting from mutations in genes encoding proteins expressed in cholangiocyte cilia. The most important of these conditions include: (i) ADPKD, caused by mutations in either PKD1 or PKD2 genes encoding Polycystin1 and Polycystin2, respectively; and (ii) ARPKD, caused by mutations in PKHD1, the gene encoding Fibrocystin. ADPKD is characterized by progressive liver cysts while ARPKD is associated with biliary cystogenesis and hepatic fibrosis. The mechanisms involved in hepatic cystogenesis in the cholangiociliopathies remain obscure but likely include abnormalities in cholangiocyte water and solute transport, proliferation, bile duct morphogenesis, and cell-matrix interactions. Our preliminary data utilizing novel in vitro experimental methods and in vivo rodent models support the notion that hepatic cystogenesis is due in part to disturbances in the normal interactions of biliary constituents with cholangiocyte cilia, altered second messenger pathways, modified miRNA post-transcriptional regulation, cholangiocyte benign hyperproliferation, and ductal dysmorphogenesis, all potential therapeutic targets.

In addition, we also study the molecular interactions between microbial pathogens and cholangiocytes. Under normal physiological conditions, cholangiocytes function as a secretory/absorptive epithelial layer modifying bile flow and composition. However, upon pathogen recognition, cholangiocytes actively participate in host defense responses. Therefore, upon pathogen recognition, the expression of immune associated genes is upregulated. We have particular interest in the Biodefense Category B Priority Pathogen, Cryptosporidium parvum (C. parvum). In immunocompetent individuals, infection is limited to the intestine and causes acute, self-limited disease. However, in the immunosuppressed, particularly those individuals with AIDS, biliary cryptosporidiosis is associated with potentially fatal complications including sclerosing cholangitis. Our current work focuses on cholangiocyte recognition of microbial pathogens and interrogates the molecular mechanisms involved in the initiation of a defense response, including transcriptional (NfkB activation) and post-transcriptional (microRNA) regulation of immune response-associated genes expressed by cholangiocytes. Our experiments utilize novel in vitro and in vivo models of biliary cryptosporidiosis to understand the molecular mechanisms of cholangiocyte recognition and response to microbial pathogens.